Chlamydomonas reinhardtii is a unicellular eukaryotic alga which possesses a CO₂-concentrating mechanism (CCM) that enables it to grow at low CO₂ concentrations. Previously, insertional mutants were generated to enable isolation of inorganic carbon transporters and other proteins that might be essential for a functional CCM. These mutants have an antibiotic resistance gene that encodes a protein that binds to Zeocin inhibiting Zeocin’s DNA strand cleavage activity. The DNA flanking the Ble^R insert of one of the high CO₂ requiring strains, named cia7, was cloned with inverse-PCR and sequenced. Sequence analysis showed homology to conserved bacterial proteins of unknown function, but there were no ESTs in this region of the genome. However, the presence of a gene was established by PCR and RLM-RACE. CIA7 was found to have four exons and the Ble^R insert was in the fourth exon. CIA7 encodes a protein of 104 amino acids with a calculated molecular mass of 11.3 kDa. Based on the ChloroP prediction program, the protein is predicted to have a chloroplast targeting signal. Complementation analyses results showed possible partially rescued mutants, and RNAi showed several transformants with a sick on low CO₂ phenotype with reduced expression of CIA7. These results suggest that CIA7 is a gene that facilitates growth in C. reinhardtii under low CO₂ conditions. One possible role of CIA7 would be in the delivery or storage of a metal ion. It may play a potential role as either a domain of a metal transporter or as a metallochaperone.